Germline Mutations of Holliday Junction Resolvase Genes in Multiple Primary Malignancies Involving Lung Cancer Lead to PARP Inhibitor Sensitization

PURPOSE

The incidence of multiple primary malignancies (MPM) involving lung cancer has increased in recent decades. There is an urgent need to clarify the genetic profile of such patients and explore more efficacious therapy for them.

EXPERIMENTAL DESIGN

Peripheral blood samples from MPM involving patients with lung cancer were assessed by whole-exome sequencing (WES), and the identified variants were referenced for pathogenicity using the public available database. Pathway enrichment analysis of mutated genes was performed to identify the most relevant pathway. Next, the effects of mutations in relevant pathway on function and response to targeted drugs were verified by in vitro and in vivo experiments.

RESULTS

Germline exomes of 71 patients diagnosed with MPM involving lung cancer were sequenced. Pathway enrichment analysis shows that the homologous recombination repair (HRR) pathway has the strongest correlation. Moreover, HRR genes, especially key Holliday junction resolvases (HJR) genes (GEN1, BLM, SXL4, and RMI1), were most frequently mutated, unlike the status in the samples from patients with lung cancer only. Next, we identified a total of seven mutations in HJR genes led to homologous recombination DNA repair deficiency and rendered lung cancer cells sensitive to PARP inhibitor treatment, both in vitro and in vivo.

CONCLUSIONS

This is the first study to map the profile of germline mutations in patients with MPM involving lung cancer. This study may shed light on early prevention and novel targeted therapies for MPM involving patients with lung cancer with HJR mutations.

LncRNA AGPG Confers Endocrine Resistance in Breast Cancer by Promoting E2F1 Activity

Resistance to endocrine therapy represents a major concern for patients with estrogen receptor α-positive (ERα+) breast cancer. Endocrine therapy resistance is commonly mediated by activated E2F signaling. A better understanding of the mechanisms governing E2F1 activity in resistant cells could reveal strategies for overcoming resistance. Here, we identified the long noncoding RNA (lncRNA) actin gamma 1 pseudogene 25 (AGPG) as a regulator of E2F1 activity in endocrine-resistant breast cancer. Expression of AGPG was increased in endocrine-resistant breast cancer cells, which was driven by epigenomic activation of an enhancer. AGPG was also abnormally upregulated in patient breast tumors, especially in the luminal B subtype, and high AGPG expression was associated with poor survival of patients with ERα+ breast cancer receiving endocrine therapy. The upregulation of AGPG mediated resistance to endocrine therapy and cyclin-dependent kinase 4/6 inhibition in breast cancer cells. Mechanistically, AGPG physically interacted with PURα, thus releasing E2F1 from PURα and leading to E2F1 signaling activation in ERα+ breast cancer cells. In patients with breast cancer, E2F1 target genes were positively and negatively correlated with expression of AGPG and PURα, respectively. Coadministration of chemically modified AGPG siRNA and tamoxifen strongly suppressed tumor growth in endocrine-resistant cell line-derived xenografts. Together, these results demonstrate that AGPG can drive endocrine therapy resistance and indicate that it is a promising biomarker and potential therapeutic target in breast cancer.

SIGNIFICANCE

Blockade of formation of the PURα/E2F1 complex by lncRNA AGPG activates E2F1 and promotes endocrine resistance, providing potential strategies for combatting endocrine-resistant breast cancer.